Heater control



Dec. 29. 1953 w. J. F. O'CONNOR ETAL 2,664,245

HEATER CONTROL Filed March 11, 1949 2 SheetsSheet l ,INVEN TORS Ward.117060/27207' ATT Y Dec. 29, 1953 w. J. F. O'CONNOR ETAL 5 HEATERCONTROL Filed March 11. 1949 2 sheets-sheet 2 ATTO VEY Patented Dec. 29,1953 Ward J. F. O'Connor and'Frank A. Rowen, .lr.,

Bayonne, N. 3., assignors to The Lummus Company, New York, N. Y., acorporation of Dela- Ware Application March 11, 1949, Serial No. 80,852

4. Claims. (o1. 236-14) This invention relates to the pyrolyticconversion of hydrocarbons in which the hydrocarbon charge is passedthrough the conversion appa ratus in an attenuated stream underconditions of temperature and pressure suitable to perform cracking.More particularly, the invention is concerned with automatic control ofthe combus tion in refinery heaters employed in such conversion, and toan arrangement whereby continuous automatic correlation is maintainedbetween the rate of flow of the entering charge of hydrocarbons, thetemperature of the outgoing conversion products, the fuel flow and theoxygen content of the products of combustion in such manner as toaccomplish maximum fuel conservation and uniform process control.

It has long been recognized that for efiicient and economical operationof refinery heaters it is essential that the combustion be accuratelycontrolled so as to maintain the most economical ratio between the rateof flow of the incoming charge and the rate of fuel flow into theheater, always assuming the maintenance of the desired temperature ofthe outgoing conversion products. While the existence of the fuel flowcontrol problem has long been recognized, its solution in the form ofautomatic control of chemical processing equipment has never, so far asthe applicants are advised, been attained until the present time. Insuch equipment, it is not only necessary to maintain generally uniformconditions but, due to the large quantities of materials handled, it isessential that changes be anticipated to prevent hunting orover-correction.

Our invention is thus largely one relating to supplemental control ofprimary controls whereby transient corrections may be made, suchtransient corrections tending to fade away under certain conditions toavoid over-actuation of a primary control.

The principal feature of our invention is the provision of standardforms of multiple chamber relays which are appropriately connected tovariable condition sensing devices in such a manner that certain changesof conditions will result in an instantaneous change in the controlswhereas certain other variables may have only a partial or temporaryeffect on the principal control.

As a secondary feature of our invention, we contemplate the use of anoxygen analysis and recording controller which will efficiently controlthe combustion air in'the combustion chamber.

Further objects and advantages of our invention will appear from thefollowing description of a preferred form of embodiment thereof taken inconnection with the attached drawing illustrative thereof, in which:

Figure 1 is a schematic control diagram for a multiple coil heater.

Figure 2 is a schematic detail of a relay valve.

Fig. 3 is a schematic outline of one embodiment of the control diagram.

In accordance with our invention, the multiple coil petroleum heaterindicated at it] has the separate heating coils l i and i2 to which thecharge inlet streams l3 and it are separately connected. The dischargeof said streams is at it and it respectively. They are generally heatedin a common furnace although there are individual rows of fuel burnersi9 and it which in turn are supplied with fuel from lines 2! and 22respectively. Fuel line 2i has a valve 23 of the double diaphragmcontrol type, the lower diaphragm being directly affected by theupstream fuel pressure through line 25. This provides a normal uniformflow of fuel. In a similar manner, fuel line 22 is controlled by valve 21, which in turn is connected through line 2% with the upstream fuelpressure.

Charge flow control is maintained through charge flow valves 3! and 52on the respective lines l3 and Id and to maintain automatic control,flow transmitters 33 and 34 are connected across customary orifice unitsand 35 respectively. Generally, the transmitter 33 supplied by air froma common source 8 is connected through line 31 with a charge flowcontrol recording meter 39, and thence through line 4i, directlycontrols flow control valve 3!. Similarly, transmitter 34 is connectedthrough line 38 with charge flow control recording meter 49 and thencethrough line 42, it controls valve 32. This provides uniform charge flowas well as providing a record of the various streams.

Any variations in the charge flow rate must be reflected in the fuelflow to avoid temperature changes in the outlet which would of course,reflect. improper heating. Charge flow conditions of line It are in turnreflected in line 37, and through line 5 i, the derivative relay i9 isaffected. The details of a relay of this type are shown in Figure 2which will be described hereinafter. It is sufficient for the presentpurpose however, to note that through line ll, the effects are carriedthrough the manual control 2? and thence through line Ml, the fuel valve23 will be controlled.

In a similar manner, the charge flOW conditions of line it which arereflected in line 38, may be impressed-by line 52, through relay 5t, andin turn, through line is, manual controller 28, and line i iil, to valveit. It is of course to be understood that the manual controllers 21 and28 may be used for temporary manual control, if desired, but ordinarilythey merely carry the automatic responses of the relays i9 and 50 to therespective valves.

Any variation in the fuel llow materially affects the efdciency ofcombustion within the heater iii and we that a variation of the positionof the heater damper t5, by damper motor should reflect a fuel valvechange. This is also accomplished through the operation'fofderivativerelay t9. Changes in fuel valveditsare -.also eiiective online if; interconnected with4averaging' relay 55. This in turn affectsline 5'1 connected. with the third derivative relay 5E, andsiniturnthrough line 6i, and manual controller 63, affects the pressure in lineat connected to the dampermotor l5.

.Ina similar manner, variations inpressurein line 3s which are appliedby line vlizto derivative relay are carried through line-t l toaveraging relay 55 to eiiect the position of damper motor However, asthe averaging relay 525 is controlled byboth fuel Ws, iit necessarilypositions the damper in accordance with anynetincrease or decrease inthe fuel flow. there is but a single stack fitiior the heater, this isthe desired objective.

By reference to Figure 2, the operation'offia derivative type relay willbe understood. In general, it includes 'a central valve-stem lilwhich isadjustably controlled by screw 5 I, such. valve stempassing through fourcompartments generally indicated A,'B, C, and D. Each of these ispressure tight, pressure in A tending tolower the stem. Pressure inB'tends to raise .the stem; pressure in C tends to lower the stem as inA, and pressure in D acts thesame as inB, toraise the stem.

When stem it moves downwardly it :will engage valve control arm l2 whichis :centrally pivoted. As arranged, th downward movement of stem 78tends to move the arm l2 into a;po-

sition to open valve 73 and close bleeder valve it. When the stem itmoves upwardly valve i l will permit discharge of pressure from chamberD.

Assuming a balanced pressure system with the position of stem ill beingheld down by spring l5, the air supply from common source-'8 dischargesfrom chamber D through orifice l6. If any change of pressure in chamber.A,. "B, :or

C is eifected, the stem will move either :upcr

down, based on the net effect, and-ifit moves up, the leakage valve T lopens to ireduce'ithe pressure in chamber D. It will thus be seen thatdifferential elfects may be obtained by'merely varying the arrangementof connections to the chambers.

Inaddition, for derivative ,j purposes as hereinafter described, we alsoprovide afib'y pass valve it between chambers B and C, 'with anadjustable needle valve 78 to controlflow therethrough. Generally,compartment B is provided with a fixed air reservoir'lg. as shown inlfigurel.

Referring again to Figure 1, fuel flow is not only a function of chargeflow, but it is also primarily a function of charge outlet temperature.Temperature recording controller 8! is thussensitive through line 83with'the outlet temperature in line it and this inturn isreheatedthrough line 85 to chamber A .ofderivative relay 49. This will cause animmediate effect on the fuel flow valve 23.

In a similar manner, temperature recording controller 82 is sensitivethrough line 84 with the outlet temperature in line l6, and is connectedwith derivative relay 50 through line 86 to effect the positioning offuel valve 24.

There isone further instrument of. major importance and that is theoxygen percentage re- ;cording controller 99. This is sensitive to theoxygen conditions in the stack as at 9! through line stand the responseis superimposed on the derivative relaytsthrough line 93.

It willthus beiappreciated that as soon as a slight change intemperatureof charge outlet 15 or IE, is noted, relays 49 and 58 will immediatelybegin to reposition the fuel valve 23 or 24. But

'as long as the rate of correction as a result of .minuteitemperaturedeviation is equal to the rate at which the flow impulse correctionvanishes,- essentially straight lin -controlwill obtain.

. In a similar .mannera slight change in oxygen content detected bytheoxygen controlling recorder. will begin repositioning the stackcamper.

.Durmg periods or constant fiow rate the output of uerivativerelays iand tilwill be identical with the output of the primary controllers is!and 32. If however there isa change in.outputof either temperaturerecording control, there will:be a.reposit1on of :the stack damper independentlyor the now-rate. The corrections to the damperpositionfromthissource aresimllarly arranged to vanish with time, but ata rate which will permit the oxygen controlling recorder to maintainessentiallyustraight line control.

The oil heater iiLof itheusual refineryisin the nature of a pressurechamber, the air for combustion being controlled effectively .bytheposition of thestackoamper d5. :Noother-control of combustionair is thusnecessary.

. In summary, it will 'benoted that we. have provided simple controlsfor .a multiple coilipetroleum or other chemical heater and that.uniformity of conversion conditions such ascracking, vaporizing or.merelysuperheating can'be readily maintained and changes promptly.compensatedfor. Provision is made for a uniform charge now by meansofthe orifice and valve setting.

Fuel flow is controlled by' the chargeflowand the outlet temperature.Inaddition, eificient oxygen control is eflected by controlling thedamper position. Uniformity between themspective streams is alsoprovided by. the averaging relay. As .a result the uniform processing ofstreams is automatically accomplished.

Having thus describedrthe invention, what is claimed is:

.1. Apneum'atioally operated control system-for a fuel fired heater or afluid charge, said heater having a charge inlet, acharge outlet, meansto introduce a fuel to said heater for-combustion therein temiera'ture.responsive means in communi ion with the charge outlet, an orifice cotrol in the charge inlet and a fuel feed control in the fuelintroduction means, said fuel feed control being adapted to maintainconstant fuel feed rate to said said system including pneumaticallyoperated relay having a "valve maintained in a central position by theinfluence of a fluid pressure source which isibalanced by a 7 spring,said relay being interconnected .to said temperature responsive meansand to said fuel feed control to vary'the: fuel reed withxrespect totemperature changes on the charge outlet, said relay having two chamberscontaining opposed pressure responsive members acting in opposition onsaid valve, mean for feeding impulses due to inlet charge flow changesdirectly to one of said chambers, and throttle valve means for applyingsaid charge flow impulse to the other of said chambers whereby transientchanges in the inlet charge flow rate will produce a relay outputimpulse to initially vary the fuel flow and then rapidly nullify saidcharge flow impulse.

2. A pneumatically operated control system as claimed in claim 1 inwhich the heater has a stack outlet for products of combustion, a damperin said outlet, a combustion gas analyzer in communication with thestack outlet, and a second pneumatically operated relay having a valvemaintained in a central position by the influence of a second fluidpressure source which is balanced by a spring, said second relay beinginterconnected to said gas analyzer and to said damper to vary thedamper position with respect to changes in the combustion gas analyzer,said relay also being in communication between the second fluid pressuresource and the output impulse of the first mentioned relay wherebytransient changes in fuel flow will initially vary the damper positionand then be rapidly damped out.

3. A pneumatically operated control system as claimed in claim 2 inwhich the heater is provided with at least two charge inlets and atleast two charge outlets for independent charge streams and each chargestream has the temperature responsive means on the charge outlet and hasseparate pneumatic relays in communication with said temperatureresponsive means and the separate fuel introduction means, and anaveraging relay interconnected with said separate pneumatic relays andwith said second relay whereby the pneumatic pressure corresponding tothe average change of fuel rate effected by said separate relays isimpressed on the second Number Name Date 1,615,481 Poole h Jan. 25, 19271,644,123 Griswold Oct. 4, 1927 1,806,597 De Florez May 26, 19311,833,153 Brown Nov. 24, 1931 1,893,635 Poole Jan. 10, 1933 1,895,701Brown Jan, 31, 1933 2,000,235 Krogh May 7, 1935 2,217,636 Rude Oct, 8,1940 2,217,637 Junkins Oct. 8, 1940 2,217,642 Luhrs Oct. 8, 19402,232,219 Dueringer Feb. 18, 1941 2,315,527 Junkins et a1. Apr. 6, 19432,337,851 Junkins Dec. 28, 1943. 2,586,503 Barnard Feb. 19, 1952 '6relay affecting the damper and is immediately damped out.

4. A system for controlling the operation of a heater to maintain thetemperature of a medium heated thereby at a constant value comprising,in combination, means for measuring the temperature of the heatedmedium, means for regulating the supply of fuel to the heater, means formeasuring the flow of process medium through the heater, means forregulating the draft through the heater, means for measuring the oxygencontent of the gases of combustion, means jointly responsive to saidtemperature measuring means and said process medium flow measuring meansoperating said fuel supply regulating means, and means responsive tosaid oxygen measuring means and to said jointly responsive meansoperating said draft regulating means.

WARD J. F. OCONNOR.

FRANK A. ROWEN, JR.

References Cited in the file of this patent- UNITED STATES PATENTS OTHERREFERENCES Rude et al., Refined and Natural Gasoline Manufacture, vol.18, No. 7, pages 255-266, July 1939.

